This invention relates to a system for controlling an engine torque, and more particularly to improvements in a device for controlling an engine torque, wherein an engine torque is changed by predetermined values during shifting to satisfactorily maintain the shift characteristics of an automatic transmission.
There is known an automatic transmission for a vehicle, constructed such that a gear mechanism and a plurality of frictionally engaging devices are provided, and a hydraulic control system is operated to selectively change the engagement of the frictionally engaging devices, to thereby achieve any one of a plurality of gear stages.
There have been also proposed many methods of integrally controlling the automatic transmission and the engine, wherein, an engine torque is changed during shifting (e.g. Japanese Patent application Laid-Open (Kokai) No. 67738/1980). When a torque transmitted quantity from the engine is changed during shifting, an amount of absorbed energy in members of the automatic transmission or in the frictionally engaging devices for controlling these members caan be decreased, so that the shifting is completed with a small shift shock for a short period of time. As a result, a satisfactory shift feeling can be given to a driver, and the frictionally engaging devices can be improved in durability.
However, when a method of delaying the ignition timing is adopted as means for changing (reducing) the engine torque for example, so-called after-burning is increased due to the delay in the ignition timing, a problem is presented such that the temperature in the exhaust system is raised. On the other hand, sometimes the engine torque is increased depending on the types of shifting, however, in this case, for example, when a method of increasing a fuel supply quantity or an intake air quantity is adopted as a method of changing (increasing) the engine torque, the temperature in the exhaust system is also raised in general.
The rise in the temperature in the exhaust system, which is caused due to the engine torque control during shifting, presents no problem if the shift frequency is normal. However, when the engine is running in a mountainous district where the shift frequency is high, or on-off accelerator operations are intentionally performed by a user for example, the temperature in the exhaust system is raised to more than a tolerance value, and in an extreme case, there is the possiblity of causing cracks in an exhaust manifold, deterioration of a catalyst, damages to a turbine blade of turbocharger, and the like.
Furthermore, when the changes in the engine torque are performed with a very high frequency, particularly, when torque decreasing control is performed, a method of suppressing the original combustion of the engine, such as an ignition timing retard, is carried out. Under these circumstances, the fuel consumption rate is worsened, the content of exhaust gas are increased to more than a specified value and so on.
As a consequence, in designing an engine torque control routine, in setting a map of engine torque change values and so on, it is necessary that no problems occur as a result of the temperature in the exhaust system, fuel consumption rate, and exhaust gas contents, even when shifting would be performed with the anticipated highest frequency.
However, when the torque change values in the map for engine torque control are set at slightly low values obviate the above-identified disadvantages, the original purpose of control for improving the shift characteristics (including the durability of frictionally engaging devices) may not be satisfactorily achieved.